In a typical combine the grain loss at the shoe and at the walker increases exponentially with feedrate. Variations in crop density during combine operation directly change feedrate, and consequently the grain loss varies. Since feedrate is also a direct function of combine speed, the combine operator can offset such change in loss by altering the operating speed. In an attempt to minimize the human error in monitoring the separation process, grain loss monitors have been developed of the type disclosed in U.S. Pat. No. 3,593,720 to J. R. Botterill and U.S. Pat. No. 3,606,745 to J. C. F. Girodat which detect the number of grain kernels passing per unit time at the discharge end of the walker or of the shoe. However, such known monitors do not indicate whether the combine is being used to maximum processing efficiency since they do not take combine ground speed into account. Grain loss monitors which measure the number of grains passing a sensor per unit time may read 1 at a 1 mile per hour (mph) which is equivalent to a reading of 3 at 3 mph and a reading of 5 at 5 mph. Five times the acreage is covered by the combine in 1 hour at 5 mph as compared to 1 mph, and the grain loss is spread over five times the area, and consequently, the processing efficiency is five times higher at 5 mph than at 1 mph.
It is common practice to judge processing quality by measuring loss per area which actually is the number of kernels per acre after processing. The combine operator cannot sense the loss per area and thus cannot accurately adjust combine speed so as to maintain the same processing quality in the presence of crop variations. The use of loss per acre as a measure of processing quality is an optimal type control in that increased loss presents a cost to the farmer while operation at a lower than acceptable feedrate extends the time required for harvesting and the number of machine operating hours.